This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The Fe-S cluster of the Rieske protein contains two ligated histidines with the Fe1. The special feature makes it highly possible to involve in not only in the electron transfer, but also in the proton transfer in various kinds of chemical reactions, such as oxidative phosphorylation, photosythesis, biodegradation etc. Since the two histidines are key residues of the redox potential, the pKa of these two are showed to affect the redox potential. Our approach is to watch for the hyperfine shift to get detailed information available exclusively from NMR spectroscopy. In order to know these information, we also need to find ways to assign the two histidines and all the closely related nuclei if they are observable in the spectra. These experiments may be keys to the electron transportation and the proton shuffle in the complex(es).